Inkjet printing on textile pieces is well known. In the direct printing method, the “construction” of the image is achieved by placing ink drops on the textile at different adjacent sites as discreet, physically non-mixed drops. In the transfer method, the colored image is first applied on the transfer media (paper that has very low affinity to the ink). The colored image is dried and then transferred to the textile piece, as by various heat transfer processes. This printing method is satisfactory for printing on light colored textile pieces. The human eye includes cells, called cones, which are sensitive to light of a particular range of wavelengths, and respond to blue light, green light and red light. All other colors we see are combinations of these three colors.
In imaging systems, colors can be mixed in different ways to produce a desired result for the eye. The mixing method commonly used in printing is known as subtractive primary colors model. In the subtractive color mixing process, colors are mixed, for example, from the primary colors cyan, magenta and yellow, using a process of subtraction or filtering. The color perceived is not generated directly by the object we observe, but rather the color seen is the result of the surrounding light being reflected off the printed ink surface, or transmitted to the substrate surface and reflected back to the viewer through the ink. The ink absorbs some, but not all of the light wavelengths, reflecting or allowing transmission of the rest. As a result, the ink film serves as a filter that selectively subtracts certain colors.
Opaque inks reflect light wavelengths, while transparent inks transmit light wavelengths to the substrate. Therefore, when using transparent inks, the substrate color is usually opaque white, or at least light. In that case, the viewer receives the reflected light from the substrate. For example, if a white substrate is painted with blue transparent ink, the ink layer absorbs the ambient light, allowing only the blue light to be transmitted to the substrate. The blue light is then reflected by the opaque white substrate, back through the ink and into the viewer's eyes, and perceive by the viewer as blue color.
However, colored images on colored backgrounds can rarely be distinguished. This is due to the fact that light impinging on the dark textile is not reflected towards the eyes of the viewer. Rather, if the substrate base color is dark, then transmitted light will be absorbed and not reflected by the substrate, and the viewer will not see the light. Thus, printing on a dark garment is not available using digital devices, such as color copiers, ink-jet printers, laser printers and the like.